1. Field of the Invention
The present invention generally relates to a network system including a mobile communications system, and in particular to an access method which provides a mobile terminal with access to a host computer of the mobile terminal through the mobile communications system.
2. Description of the Related Art
In radio mobile communications, a plurality of data exchanges are needed for connection establishment between a mobile terminal and a connection control station. To achieve rapid connection establishment, there has been proposed a call connection procedure in Japanese Patent Unexamined Publication No. 4-23527. More specifically, when calling, the mobile terminal transmits a calling signal conveying a source ID (identification) number, a destination ID number, and additional information to the connection control station. In the connection control, the following processes are performed concurrently: a subscriber information check using the source ID number, an additional information check, and a connection process of a switching system. Only when all responses to the checks and the connection process are affirmative, the connection between the mobile terminal and the connection control station is established.
An authentication method using secret-key encryption has been proposed in Japanese Patent Unexamined Publication No. 5-183507. An ID center transmits random data as an authentication request signal to a mobile terminal. At the mobile terminal, the received random data and a secret key input by the subscriber are used to produced encrypted data. The encrypted data is transmitted as an authentication response signal to the ID center. At the ID center, the random data and a registered secret key are used to produce encrypted data which is compared with the received encrypted data from the mobile terminal. If the produced encrypted data is coincident with the received one, the authentication check is affirmative.
Similarly, a radio telephone service access method using secret-key encryption has been proposed in Japanese Patent Unexamined Publication No. 4-2333341.
In the case of a host access system in which a mobile terminal obtains access to a host computer through the mobile communication system, however, the conventional technique described above fails to provide both sufficiently rapid connection establishment and sufficient security of private information. In the connection control procedure where a calling signal conveying a source ID number, a destination ID number and additional information is transmitted to the connection control station, after all the necessary check processes have been completed in the mobile communication system, the connection between the mobile terminal and the host computer is established. In other words, the connection cannot be established without completing all the necessary check processes in the mobile communication system.
In the conventional authentication methods using secret-key encryption, a plurality of data exchanges are needed for connection establishment between a mobile terminal and a connection control station. Therefore, it is very difficult to shorten the time required for connection establishment.